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Lots of kids are afraid of the dark, and some adults still can't stand sleeping in the complete darkness. But why are we afraid of it?

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[♩ INTRO].

Were you scared of the dark growing up? Or maybe you still are!

It's not too uncommon for adults either. When you're young, being afraid of the dark goes hand in hand with some other fears, like of ghosts, monsters, or other spooky things. And as you get older, you might not use that sort of explanation anymore.

But these irrational fears still stick around, because there are a lot of ways we learn to be afraid. The good news is: research has found out that there are ways to fight those fears, too. The way we usually develop fears is a well-understood part of psychology.

Most of the time, it's through classical conditioning. This is when you pair a neutral stimulus — something that doesn’t make you feel anything — with something that you have an automatic reaction to. Like, imagine a person who's generally cool with dogs.

But then, a dog bites her and she has to go to the hospital. That’d make anybody freak out a bit. Then, the neutral stimulus can become a conditioned stimulus, which gives you the same automatic reaction.

In other words, after that experience, this person is more likely to be afraid when she sees a dog. Some phobias, which are extreme or irrational fears, can be caused by classical conditioning, including a fear of the dark. Research in animals and humans has found that conditioned responses are probably linked with the amygdala.

That’s a brain region that becomes active when people are afraid, or have a lot of high-arousal emotions, like excitement and anger. So conditioned fears kind of make sense: they’re based on something that happened to you. And some surveys have found that most children have had a bad experience with the thing they’re scared of, like spiders or the dark.

But other phobias are of things that you’ve never actually experienced. Like, arachnophobia is one of the top fears in the world, but most people haven’t actually been attacked by spiders. Some survey results, including one sample of over 1,000 children and teenagers, suggest that we might learn these fears because of modeling.

Like, when your older brother sees a spider and freaks out, so you do too. Or, where shark attacks are a huge threat, or a horror movie where the killer lurks in the darkness. Even more common in that survey was learning through instructional fear acquisition — when someone tells you to be afraid of something.

This can happen if your mom warns you to watch out for snakes, or when news broadcasters talk about terrorist attacks, even though the actual statistics say you're much more likely to die of something like a heart attack. This is because people tend to use an availability heuristic in their reasoning, meaning they use what’s readily available to their mind. It’s hard to remember the exact statistics about terrorism and heart disease, but boy, that last story you saw on the news sticks with you.

And it probably wasn’t about a heart attack. In fact, when researchers run studies and try to condition people to fear something neutral — like associating a certain tone with a mild shock — they're more successful if they tell people what to be afraid of beforehand. Now, across all these studies, some psychologists noticed a weird pattern: some phobias are easier to create than others in certain species.

For example, scientists have observed that it's easier for primates to develop a fear of snakes or spiders — but not of something like rabbits. They call this phenomenon biological preparedness. We can't say for sure why it happens, but one idea is that these fears are somehow ingrained from our ancestors’ behaviors.

Like, all mammals might be more wary around snakes and lizards, because the first mammals could’ve been eaten by ancient reptiles. Some ecologists looked into an evolutionary reason for fearing the dark, based on a risk from predators, by studying some regions of Tanzania where lion attacks are a threat to humans. Using data from over two decades and over a thousand lion attacks, they found that most attacks occurred right after sunset, when it’s dark but people are still wandering around.

But they also found that attacks were up to four times more common in the ten days after a full moon than the period before, which is when the darkest part of the night is also right after sunset. So if that pattern of lions attacking humans in the dark was also true millennia ago, it's possible that some early humans became conditioned to fear the dark or the full moon. Scientists have guessed that people might be predisposed to be afraid of the dark because we adapted to a risk of predator attacks.

But this is one of the first studies suggesting that darkness actually increased that risk. But it's worth taking these evolutionary hypotheses with a grain of salt. It’s not like anyone’s run a study where they assigned some people to a lion-risk condition and others to a no-lion condition, and then waited for generations to see what fears develop.

So we’ve got a couple good ideas about where phobias come from. And if you have a phobia, psychologists have found ways to treat them. Many randomized trials show that one of the most effective treatments is called exposure therapy, which is essentially just conditioning in reverse.

You slowly expose yourself to what you're afraid in small doses — like turning off the light for five seconds, being in the same room as a spider, or meeting groups of strangers — until you don’t have a bad reaction anymore. Then you move the spider a little closer, leave the lights out longer, or meet more people — until the phobia has less power over you. Now, fear is a really complicated thing.

So if you love being scared by things like horror movies, check out our video about why psychologists think that happens. And if you want to keep learning about other brain things, you can go to and subscribe. [♩ OUTRO].